This invention relates to a multi-valve engine and more particularly to a improved cylinder head construction for such engines and an improved cylinder head that can be employed as either bank of a cylinder having angularly related cylinder banks and a method of manufacturing such a cylinder head.
The advantages of multi-valve internal combustion engines are well known. Frequently two intake valves are employed for introducing the charge into the combustion chambers of the engine. By employing two intake valves rather than one intake valve of the same diameter, it is possible to obtain improved charging efficiency and performance. The two smaller valves can be opened and closed at a more rapid rate and thus permit the engine to be operated at a higher speed and actually obtain better breathing than one large single intake valve.
Recognizing the advantages of multiple intake valves, most high performance engines presently employee two intake valves per cylinder. For the same reasons that two valves have an advantage over one, the use of three intake valves have a number of advantages and can offer still further improvements in performance.
One disadvantage with the use of three rather than two intake valves is that the valve placement can cause some difficulties. Specifically, when the number of intake valves is increased, it is difficult to maintain small combustion chamber surfaces and good thermal efficiency. In addition, the surface area of the combustion chamber may increase and this also makes it difficult to maintain high compression ratios.
An arrangement has been proposed, therefore, that uses three intake valves with two side valves being disposed so that they are intersected by a plane containing the cylinder bore axis but have the major portion of them lying on one side of the plane. A third center intake valve is positioned completely on this side of the plane and is disposed between the side intake valves. The center intake valve is disposed at the outer peripheral edge of the combustion chamber and in order to maintain high compression ratios this valve reciprocates about an axis that is disposed at a very small acute angle to the plane containing the cylinder bore axis.
With this type of arrangement, it is also the practice to employee a single centrally positioned spark plug. This means that the head of the side intake valve is disposed below the gap of the spark plug and hence there is a shielded area beneath this valve when the spark plug fires. This shielded area may preclude total flame propagation across the combustion chamber and can result in incomplete burning, loss of performance and reduced exhaust emission control.
It is, therefore, a principal object of this invention to provide an improved valve arrangement for a three intake valve per cylinder engine and wherein complete combustion can occur.
It is a further object of this invention to provide an improved placement for the center intake valve of a multi-valve engine wherein the center intake valve is disposed so that total flame travel is not retarded and complete combustion can be achieved.
It is a further object of the invention to provide an improved cylinder head and combustion chamber arrangement for a multi-valve engine.
Frequently in internal combustion engines and particularly those having angularly related cylinder banks, it is the practice to employ a common cylinder head casting for both of the cylinder banks. This cylinder head casting is positioned in one orientation on one cylinder bank and is rotated through 180.degree. when attached to the other cylinder bank. This permits the induction system or exhaust system, whichever is preferred, to be disposed in the area between the cylinder banks. By using a common cylinder head casting, the number of different parts employed can be reduced and the cost therefore reduced accordingly.
In addition to using this concept on the banks of an engine having angularly related cylinder banks, with some applications it may be possible to mount the same cylinder head in either orientation on the same cylinder block and thus there may be advantages in employing one cylinder head that can be utilized with dissimilar cylinder blocks or the same cylinder block to orient the intake and exhaust passages in a different fashion.
When a common cylinder head casting is utilized and is rotated through 180.degree. for mounting depending upon the application, certain problems or compromises must be encountered. For example, when the engine is provided with an overhead cam shaft it is the normal practice to have the cam shaft extend beyond one end of the cylinder head to establish its driving relationship with the engine crankshaft. However, if the cylinder head is designed to be mounted in either direction in the cylinder block, this means that the cam shaft journals at both ends of the block must extend to the end of the head. Thus, when the cam shaft does not extend beyond one end of the head, there is a sealing problem that arises at this end of the head. This has been accommodated normally by mounting a closure plate over the end of the cylinder head at this end but this obviously adds to the cost of the engine and its complexity. Furthermore, this brings a number of surfaces together all of them which must be sealed with respect to each other.
It is, therefore, a still further object of this invention to provide an improved cylinder head assembly that adapts itself to mounting in either of two orientations on a cylinder block while minimizing the sealing problems.
It is a further object of this invention to provide an improved method for forming a cylinder head which can be employed for mounting in either of two orientations on a cylinder block.
In engines having angularly related cylinder banks it is generally the practice to stagger one bank slightly relative to the other bank. This staggering is done so that corresponding connecting rods of the respective cylinder banks can be journaled on the same journal of the crankshaft. This permits a simpler crankshaft assembly and actually permits shortening of the overall length of the engine.
Where the cylinder block banks are staggered relative to each other and where a common cylinder head used for each bank, with the constructions heretofore proposed the cylinder heads have also been staggered relative to each other. Thus, if each cylinder head journals at least one overhead cam shaft then one of these cam shafts will be displaced rearwardly from the other due to the cylinder head configuration. This gives rise to difficulties in not only driving the cam shaft but also can complicate the overall engine structure, particularly when it is desired to mount the timing drive for the cam shafts within a common housing.
It is, therefore, a still further object of this invention to provide an improved cylinder head construction which permits mounting in either of two 180.degree. displaced orientations and wherein one end of the cylinder head is configured so as to accommodate the offsetting when used with engines having two cylinder banks.